This invention relates to motor controllers and, more particularly, motor controllers which function to terminate power to a motor in response to various detected fault conditions.
Motor controllers function to terminate power to a motor in the event of various fault conditions. These fault conditions result from a variety of factors, such as the motor being jammed or stalled, the motor being underloaded or the motor losing the normal relationship of its three phases. These conditions are detected by monitoring the current to the motor for characteristics, such as excess current, which are associated with the fault conditions. When these fault conditions are detected, the controller functions to terminate power to the motor.
Unfortunately, these same fault conditions often normally occur temporarily during start-up of the motor. During start-up of the motor, it is desirable to permit these conditions to exist without causing the controller to terminate power, or to trip out.
A possible solution to this problem is to disable the power terminating means for a preselected time period after initiation of motor starting. The motor start-up time will vary among different motors, and more importantly, will also vary time to time in the same motor under different motor loads or other operating conditions. Accordingly, the preselected time period for a given motor, or for given motor condition, may be too long or too short for a different motor or for the same motor under different conditions. If the time period is too long, then the motor will be unprotected for a portion of that time. On the other hand, if the time period is too short, inadvertent power termination will occur during start-up.
Accordingly, a need exists for means to prevent inadvertent power termination by a controller in response to fault conditions during start-up which is not based upon any particular time period for start-up of the motor.